The present invention relates to a rotor angle detecting apparatus for a reluctance motor, which is capable of detecting the rotational angle of rotor core and/or rotor shaft of a reluctance motor.
There is a conventional encoder capable of detecting a rotational angle of a rotor core. This encoder has a magnet attached to an axial end surface of the rotor core and a magnetism detecting element disposed adjacently to this magnet in the axial direction. The magnetism detecting element detects variations of magnetism occurring in this magnet. The magnetic forces generating from this magnet are inverse proportional to the square of distance. Thus, the axial gap between the magnet and the magnetism detecting element must be accurately adjusted to assure reliable detection accuracy of the encoder. Hence, as shown in FIG. 1A, the gap (i.e. distance) between a magnet J1 and a magnetism detecting element J2 should be maintained at a pre-designated appropriate distance, for example, by performing a shim adjustment or the like during assembling processes of this motor.
The reluctance motor has a rotor core J3 causing rotations based on magnetic attractions between outward salient-poles J4 (having lower magnetic reluctances) of the rotor core J3 and inward salient-poles J6 of the stator core J5. More specifically, successively switching the combination of inward salient-poles J6 generating magnetomotive forces causes the rotor core J3 to rotate about its rotation center. Therefore, as shown in FIG. 1A, the stator core J5 should be completely opposed to the rotor core J3 in the axial direction. However, as shown in FIG. 1B, there will be the possibility that the rotor core J3 may be unwontedly offset in the axial direction relative to the stator core J5 and, as a result, the rotor core J3 may be dislocated toward the magnetism detecting element J2. In such a case, when the motor is operating (i.e. when electric power is supplied to the coils to generate magnetomotive forces from the inward salient-poles J6), the magnetomotive forces of the stator core J5 will undesirably induce a thrust force X (shown by an arrow) acting on the rotor core J3. If the rotor core J3 is subjected to the thrust force X, the rotor core J3 will shift in the direction indicated by the arrow X (namely, will go away from the magnetism detecting element J2). Thus, there will be the possibility that the gap (i.e. distance) between the magnet J1 and the magnetism detecting element J2 becomes larger than the pre-designated appropriate distance.